Fine jewelry rope chains for necklaces and bracelets etc. have been known for a long time. The traditional rope chain, constructed from intertwined links soldered to one another has not changed basically over the past hundreds of years. Although rope chains are also manufactured by automatic machines, the tightly intertwined chains are still being manufactured to a great extent by hand. In my earlier patents U.S. Pat. Nos. 4,934,135 and 4,996,835, I disclosed and claimed rope chains and methods for preparing such rope chains having reduced weight and labor costs compared with conventional rope chains of the same chain diameter.
A particularly popular type of rope chain is commonly known as a diamond cut rope chain. Such a chain comprises flat cuts or facets on the outer perimeter of at least some of the chain links to provide a flat mirror finish surface which is very light reflective, making the chain sparkle. This diamond cut facet can easily be prepared on solid rope chains, i.e. chains made with solid links, by cutting or shaving a facet from the arced section of the link, as is well known in the art.
Conventional solid diamond cut (faceted) rope chains have facets generally cut about one third or more into the thickness of the chain link in order to obtain a reasonable size shiny surface, as illustrated in FIG. 1. The amount of precious metal sheared away to form this facet can account for up to 10% of the weight of the chain and although the metal shearings are collected and recycled, a significant amount of precious metal is nevertheless lost in the process. In the case of hollow rope chains, i.e. chains having hollow links, it is difficult to make diamond cut facets in the conventional way, since the outer plate of the hollow wire making up the chain link is very thin and can be as little as 0.05 mm thick, and any facet cut in the outer arced perimeter of the link would make a hole through this outer plate.
A recent patent to Strobel, U.S. Pat. No. 5,125,225, discusses the making of rope chains in general and hollow rope chains specifically and claims a method for manufacturing diamond cut hollow rope chains by wrapping a hollow rope chain about a lathe drum, freezing the drum, applying water to the chain to freeze it in place thereby immobilizing it, and advancing a blunt burnishing tool against the links of the chain by applying a plurality of incremental deformative thrusts of blunt force against some of the curved outer wall portions of the hollow links until this outer wall is deformed and pushed back towards the inner wall of the links, thus flattening portions of the curved outer wall. By rotating the lathe drum and advancing the blunt burnishing tool, additional links along the chain length receive flattened surfaces. According to this method, not all of the chain links have identical flattened area. The amount of flattened area of any link will depend on the particular position of the link in the chain when the blunt burnishing tool strikes it. Those links whose outer edge is closer to the blunt tool will have a larger flattened area, whereas the links that are further away from the blunt tool receive smaller increments of force and will therefore have smaller flattened areas. These flattened portions of the outer walls are then diamond cut to remove or shave off a very thin layer of metal (about 0.001 to 0.002 mm) to provide smooth and shiny facets without making any hole in the link. According to this patent, the hollow link undergoing the flattening process has one flat oval facet positioned approximately opposite the link gap, as illustrated in FIG. 5 of said patent, similar to conventional diamond cut solid rope chains shown in FIG. 1. The cross section of the faceted area is obviously deformed with respect to the cross-section of the rest of the chain link.